Aspects of the disclosure relate in general to the synchronization of local oscillator (LO) signals for RF carrier tuning in a distributed phased array system.
Antenna arrays offer a way of increasing the data rate and the signal to noise ratio of a received or transmitted beam. When an antenna array is used to transmit a steered beam, the time, phase, and/or relative amplitude of the signal at each antenna is controlled in order to create a pattern of constructive and destructive interference. When receiving a steered beam, information from different antennas is combined in such a way that the expected pattern of radiation is preferentially observed.
When a signal is coming from a direction that is not orthogonal to the plane of a planar antenna array, the signal arrives at the different array antennas at different times. By adjusting the relative times that samples are taken from the received signal at the different array elements, the system can be electronically steered so as to reject energy not coming from the direction of the incoming signal. This increases the signal to noise ratio and can enable higher data rates. Similar time delay methods can be used to adjust the directionality of transmit signals.
Instead of adjusting transmission times and sampling times, phased arrays use waveforming techniques to adjust the relative phase offsets of the array elements during sampling of received signals or transmitting outgoing signals. The change in phase accomplishes an effect similar to the transmission and sampling delays, but the appropriate phase changes vary with carrier frequency. Thus, phased array systems are unsuitable for large bandwidth operations, and must be precisely tuned to a single carrier frequency.